Devices, such as constrained devices, sensors, and actuators, deployed as a network of nodes have become useful for collecting and/or processing data in applications such as ambient intelligence, smart environments, and autonomous control. For example, networked sensors may be deployed in a building to measure the temperature and humidity such that an air conditioning system for the building may be adjusted autonomously. These networked nodes are generally referred to as constrained nodes or constrained devices in a (constrained) network, and each constrained node generally has at least one resource such as temperature and humidity. The nodes may be accessible, e.g., in an Internet-like network, where each device is a uniquely identifiable node, and the nodes act as servers to which clients can connect. Such a system of nodes may be referred to colloquially as “Internet of Things”. The nodes may be in a wired network and/or a wireless network. In some situations, these nodes are constrained devices, having limited power and computing resources. The network that connects these objects may be referred to as low power and lossy networks (LLNs). Typically, each of the nodes has at least one resource. A resource may be associated with a state of the device and/or information associated with the device, or with an action that can be executed on the device. Examples of resource includes: “/temperature”, “/humidity”, “/room_location”, “/picture”, “/light_control”, etc. Clients may query the node (i.e., the server) for the resource at the node.
These networked nodes are typically constrained in their functionality and computational resources and may be referred to as “constrained devices”. With the advent of technologies such as 6lowpan, these nodes have become easily accessible over the Internet, e.g., in an Internet of Things situation. The nodes (i.e., servers) are potentially addressable by a large number of clients around the world. Some interactions between a client and a node are very short-lived (e.g., requesting the temperature). However, interaction models where, e.g., the state of a resource of a node is monitored over a longer period of time (whereby a relationship/session between the client and the server is maintained) have shown to be of importance for client applications, e.g., for use in the Internet of Things domain. Such an interaction model burdens these nodes, because the node has to maintain many server-client (data) sessions (e.g., server-client relationships) for a large number of clients. This problem is especially severe if these nodes are low in power, and an increase in load may lead to shorter lifetime for these devices.